The Effect of Spectrum-Enhanced Artificial Light on Students’ Cognitive Activities

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors

This article is impressive. The team comprises engineers and physicians, meaning the technical aspect as well as the human factors are thoroughly mastered. The basic idea is to compare two kinds of lighting w.r.t. their ability to increase the human concentration. To that end, both behavioural (attention) and evidence-based (EEG) methods are used.

The two sets of lighting systems are described as usual with CCT and illumination levels in the horizontal plane, as well as CS, m-EDI and CLA in the vertical plane.

Yet I fear one important parameter is missing. Namely flicker A.K.A. Temporal Light Modulation. It is known to have many effects, some visible (making the environment annoying) to non-visible (eye fatigue, headache, ...) IMHO in order to not delay this paper, I suggest to record both light levels with a fast photodiode and compute the relevant metrics. For a good overview I recommand reading https://www.energy.gov/sites/default/files/2023-05/ssl-miller-etal-2022-LRT-flicker-review-tlm-stimulus-response.pdf Nevertheless, flicker  will become some random disturbance in your study. So I suggest to test if your ballasts can be powered with 230 V DC using a good quality power supply. Most electronics system whose first stage is a rectifier accept DC. For the fluorescent tubes, that implies the use of an electronic ballast. In that case, tell in the conclusions that more patients will be tested, but this time under flicker-free lighting.

Another factor which should be investigated is  the Homeostat-Circadian-Light (HCL) model. May I suggest to test if the patients are roughly in the same phase of their sleep / wake pattern during the experiments ?

For the rest, most results are reported with too many decimal figures. Could you stick to the GUM recommandations ? Look f.i. on the LHS of fig.9. Test statistic of 12.000. What about 12 instead ? 

Author Response

Dear Reviewer,

Thank you for these thoughtful comments and suggestions. We truly appreciate you taking the time to share your insights, as they are very valuable in helping us improve the quality of our article.
Below, we have reproduced each point from your review and then provided our response, highlighted in yellow.
Please note that in the manuscript, we have highlighted in yellow the sections that have been modified based on your suggestions or those of other reviewers.

Yet I fear one important parameter is missing. Namely flicker A.K.A. Temporal Light Modulation. It is known to have many effects, some visible (making the environment annoying) to non-visible (eye fatigue, headache, ...) IMHO in order to not delay this paper, I suggest to record both light levels with a fast photodiode and compute the relevant metrics. For a good overview I recommend reading https://www.energy.gov/sites/default/files/2023-05/ssl-miller-etal-2022-LRT-flicker-review-tlm-stimulus-response.pdf Nevertheless, flicker will become some random disturbance in your study. So I suggest to test if your ballasts can be powered with 230 V DC using a good quality power supply. Most electronics system whose first stage is a rectifier accept DC. For the fluorescent tubes, that implies the use of an electronic ballast. In that case, tell in the conclusions that more patients will be tested, but this time under flicker-free lighting.
Thank you for your helpful suggestions and comments. We have added a paragraph (lines 783…787) highlighting the lack of flicker measurements as a limitation of the present study. We would like to incorporate these measurements into our future research or, as you suggested, use flicker-free ballasts. However, we would like to conduct thorough research and find a precise way to evaluate these effects. 
 
Another factor which should be investigated is  the Homeostat-Circadian-Light (HCL) model. May I suggest to test if the patients are roughly in the same phase of their sleep / wake pattern during the experiments ?
The manuscript specifies (lines 376-377) that all participants confirmed they had received a minimum of 7 hours of sleep on the night preceding the testing sessions.
Before each test, participants reported the number of hours slept the previous night and completed a 9-point alertness/sleepiness scale (1 extremely alert, 9 extremely sleepy). These measures were used to verify whether participants were in comparable phases of the sleep/wake cycle, according to the Homeostat-Circadian-Light (HCL) model, and whether they were rested. Based on this questionnaire, we identified that the average number of hours slept by the subjects varied between 7 hours and 7 hours and 20 minutes in all experimental stages, and in the alertness test, the results were between 4-5 (4 = fairly alert and 5 = neither alert nor sleepy). Statistical analysis did not identify any significant differences between subjects based on these variables, so it can be considered that the participants were in comparable phases of the sleep/wake cycle and were sufficiently rested in all experimental conditions. Thus, the observed effects on performance in the D2 and TP tests can be attributed with greater confidence to the type of lighting (LED vs. fluorescent) and not to variations in sleepiness or previous sleep duration.

For the rest, most results are reported with too many decimal figures. Could you stick to the GUM recommendations ? Look f.i. on the LHS of fig.9. Test statistic of 12.000. What about 12 instead ? 
As we have observed in the literature, researchers generally present these data with 2 or 3 decimal places. We have updated figures 9...14 in the old manuscript (figures 9, 10, 12, 13, 15, 16 in the new manuscript), keeping 2 decimal places. We also reduced the number of decimal places in tables 6..14. 

Kind regards,
The authors

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents a experimental investigation examining the effects of LED lighting with enhanced long-wavelength spectrum versus conventional fluorescent lighting on undergraduate students' cognitive performance. The study uses a robust multi-method approach combining neurophysiological (EEG) recordings with established psychometric tests (d2 and Toulouse-Piéron), which strengthens the validity of the findings. The authors have conducted a methodologically rigorous study addressing an important gap in lighting research. The use of multiple assessment modalities, appropriate statistical analyses for non-normal distributions, and transparent reporting of limitations demonstrate good scientific practice. The findings regarding warm-spectrum LED effects provide valuable insights for classroom lighting design. The manuscript will be suitable for publication after some minor revisions.

1. The abstract could add 1-2 introductory sentences establishing the research context and significance of investigating lighting effects on cognitive performance in educational settings.

2. The introduction provides thorough background but could be more focused for improved readability. Please focus on indoor lighting effects directly relevant to educational environments.

3. Please incorporate unit labels (cm) directly within the figure rather than only in the caption in Figure 1

4. Add labels with arrows identifying key components (controllers, signal sources, LED channels) directly in Figure 3 to enhance reader understanding of the system.

5. Consider presenting some results currently in tables (particularly Tables 6, 9, and 12 showing Wilcoxon test results) as bar charts with error bars, could provide more intuitive visualization of comparisons and effect sizes.

6. For Lines 662-668), the discussion of d2 test results could be improved by adding more definitive scientific interpretation. Rather than stating uncertainty, consider proposing specific hypotheses, such as: "The divergent d2 test results may reflect differential sensitivity of this specific attention task to spectral variations, possibly due to its emphasis on sustained visual discrimination engaging distinct attentional networks compared to the TP test."

Author Response

Dear Reviewer,

Thank you for these thoughtful comments and suggestions. We truly appreciate you taking the time to share your insights, as they are very valuable in helping us improve the quality of our article.
Below, we have reproduced each point from your review and then provided our response, highlighted in yellow.
Please note that in the manuscript, we have highlighted in yellow the sections that have been modified based on your suggestions or those of other reviewers.

1.    The abstract could add 1-2 introductory sentences establishing the research context and significance of investigating lighting effects on cognitive performance in educational settings.
We added a phrase at the beginning of the abstract: “Light is a powerful environmental factor with proven effects on human cognitive activity”.  I would like to point out that we are limited—the Abstract section has a word limit, and we had to write in a very concise manner.

2.    The introduction provides thorough background but could be more focused for improved readability. Please focus on indoor lighting effects directly relevant to educational environments.
Since the subject under study is very complex, involving many factors that characterize artificial lighting systems, we would like to keep the structure of the introduction roughly as it is, so that readers can have an overview of current research directions. However, we have added a paragraph (lines 721...762) to the Discussion section, which addresses in more detail the research most relevant to educational environments.

3.    Please incorporate unit labels (cm) directly within the figure rather than only in the caption in Figure 1
Figure 1 has been updated.

4.    Add labels with arrows identifying key components (controllers, signal sources, LED channels) directly in Figure 3 to enhance reader understanding of the system.
Figure 3 has been updated.

5.    Consider presenting some results currently in tables (particularly Tables 6, 9, and 12 showing Wilcoxon test results) as bar charts with error bars, could provide more intuitive visualization of comparisons and effect sizes.
We have chosen to present the results from Tables 6, 9, and 12 using boxplots instead of simple bar charts. This is because the statistical non-parametric test we used (the Wilcoxon test) is specifically designed to compare the typical score (the median) and the overall spread of the data, rather than just the average. We have added figures 11, 14 and 17. Please note that, compared to the previous version of the article, the index of figures has changed, starting with figure 11.

6.    For Lines 662-668), the discussion of d2 test results could be improved by adding more definitive scientific interpretation. Rather than stating uncertainty, consider proposing specific hypotheses, such as: "The divergent d2 test results may reflect differential sensitivity of this specific attention task to spectral variations, possibly due to its emphasis on sustained visual discrimination engaging distinct attentional networks compared to the TP test."
We have modified the paragraph in order to reflect this point of view (lines 690-693 in the manuscript).

Kind regards,
The authors

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

I have reviewed your manuscript titled “The effect of spectrum-enhanced artificial light on students' cognitive activities" submitted to the SUSTAINABILITY Journal under the reference sustainability-3874082. I appreciate the significant contribution of your research in the effects of lighton concentration and attention of undergraduate students. Below, I provide detailed feedback on various aspects of your paper.

 Originality / Novelty:

Your investigation of the possible effects of two types of light—LED with an enhanced long- wavelength spectrum (warm tones) and classic fluorescent—on concentration and attention of undergraduate students could allow to get insights into the effects of light on the human mind and body.

Significance of Content:

Your study explores how artificial lighting spectrum affects cognitive performance in a classroom equipped, the authors built an experimental setup consisting of two lighting conditions: i) the spectrum is richer in warm colors (towards the yellow and red part of the spectrum) and ii) a classic cold light fluorescent lighting system (with a spectrum richer in "blue" light). On the one hand, the concentration of students was assessed through neurophysiological recordings (EEG). On the other hand, attention of the same students was evaluated using two psychometric tests: the d2 Test and the Toulouse-Piéron test.

Quality of Presentation:

The manuscript is well-written and structured for understanding in an easy way your reasoning. To study the effect of artificial lighting system on cognitive activities of undergraduate university students, you built an experimental setup consisting of two lighting conditions: i) the spectrum is richer in warm colors (towards the yellow and red part of the spectrum) and ii) a classic cold light fluorescent lighting system (with a spectrum richer in "blue" light). Figures and tables are appropriately used both to present and discuss the results obtained effectively.

Scientific Soundness:

For analyzing the small sample sizes captured, the Mann–Whitney U test was applied; for evaluating the ranks of differences between paired observations, the Wilcoxon signed-rank test was used; and for evaluating both main effects and interaction of data, the f1.ld.f1 test was employed. Across all three measures, the autors found that LED lighting with a spectrum richer in warm colors can support students’ attention and concentration. This finding must be considered mainly exploratory because of the modest sample size (27 subjects for the TP and d2 tests, and 8 subjects for the EEG tests).

Interest to the Readers:

Your manuscript is a valuable foundation for future studies with larger samples, more robust experimental designs, and a deeper integration of EEG data with psychometric performance measures. Therefore, your manuscript could be of interest for academic and practitioners focused in designed lighting for a more comfortable human mind and body.

Overall Merit:

In conclusion, your manuscript "The effect of spectrum-enhanced artificial light on students' cognitive activities" is overall competent and pertinent. The originality of this study contributes significantly to the state-of-the-art about the effecst of artificial lighting system on cognitive activities of undergraduate university students. I support the publication of your manuscript to the SUSTAINABILITY Journal.

Author Response

Dear Reviewer,

Thank you for taking the time to review this article and for your appreciation of our work. 

Sincerely, 
The authors

Reviewer 4 Report

Comments and Suggestions for Authors

The article is interesting, innovative, and original from a methodological perspective. This reviewer thoroughly enjoyed reading it. The main idea of ​​quantifying the effects of lighting technology (fluorescent/LED) on students is important. The introduction is of an appropriate length and includes relevant references. In the methodology, nonparametric statistical tests are adequate, both due to the results of the normality test and the amount of data.

Here are some comments:

The authors find that "A significant effect of lighting type was found in both the EEG and PT tests: participants tested under LED light showed higher performance compared to those tested under fluorescent light," which summarizes their findings. However, LED has a CCT of ~3600K (warm white) and fluorescent has a CCT of ~5600K (cool white). The literature suggests that cooler temperatures should be used in study rooms (for example, in the Lighting Handbook, due to, among other reasons, the production of malatonin). By finding this result, the authors favor the performance of students exposed to warm light. This apparent contradiction needs to be explored further, perhaps from the perspective of "effective concentration" or exposure time, spectrums, dose, etc. It is important to compare it with studies that have found similar results.

In lines 715-724, the authors describe the limitations of the study. It is important to discuss whether these limitations may have influenced the generality of the results and, if so, where the risk of reproducibility lies.

Author Response

Dear Reviewer,

Thank you for these thoughtful comments and suggestions. We truly appreciate you taking the time to share your insights, as they are very valuable in helping us improve the quality of our article.
Below, we have reproduced each point from your review and then provided our response, highlighted in yellow.
Please note that in the manuscript, we have highlighted in yellow the sections that have been modified based on your suggestions or those of other reviewers.

The authors find that "A significant effect of lighting type was found in both the EEG and PT tests: participants tested under LED light showed higher performance compared to those tested under fluorescent light," which summarizes their findings. However, LED has a CCT of ~3600K (warm white) and fluorescent has a CCT of ~5600K (cool white). The literature suggests that cooler temperatures should be used in study rooms (for example, in the Lighting Handbook, due to, among other reasons, the production of melatonin). By finding this result, the authors favor the performance of students exposed to warm light. This apparent contradiction needs to be explored further, perhaps from the perspective of "effective concentration" or exposure time, spectrums, dose, etc. It is important to compare it with studies that have found similar results.
We have expanded the Discussion section to include a more detailed examination of the research most relevant to educational settings (see lines 721…762), providing also some potential explanations for the differences observed in comparison to other studies.

In lines 715-724, the authors describe the limitations of the study. It is important to discuss whether these limitations may have influenced the generality of the results and, if so, where the risk of reproducibility lies.
We have moved the discussion of all limitations of the current study into a new, dedicated section titled '5. Limitations of the Study' – lines 763 …791. There, we also addressed the issues you highlighted.

Kind regards,
The authors